Carbon nanotubes were first discovered and reported in an article by Sumio Iijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). Carbon nanotubes have been highlighted as a new functional material expected to have many microscopic and macroscopic applications. Extensive research has been conducted into using carbon nanotubes in various applications, e.g., in field emission devices, memory devices, gas sensors, microwave shields, electrode pole plates in electrochemical storage units, etc.
There are various kinds of methods for synthesizing carbon nanotubes, for example, arc-discharge methods, laser ablation methods and chemical vapor deposition methods. The chemical vapor deposition methods are widely used for making carbon nanotubes as they are relatively simple, inexpensive, easily mass-produced, and conducive to growing carbon nanotubes with a high level of alignment. Generally, the chemical vapor deposition methods include thermal chemical vapor deposition methods and plasma enhanced chemical vapor deposition methods. An apparatus for synthesizing carbon nanotubes using such a chemical vapor deposition usually includes a reaction chamber having a gas inlet for introducing gas and an opposite gas outlet for discharging exhausted gas. The reaction chamber is configured for receiving a catalyst therein and then providing a growth atmosphere for carbon nanotubes.
Currently, carbon nanotubes synthesized by the above-described methods usually are a mixture of carbon nanotubes having various different kinds of tip structures, includes, for example, closed tip structure and open tip structure. In particular, closed tip structures of carbon nanotubes have no dangling bond and may be hemispherical, cone-shaped or horn-shaped. Open tip structures of carbon nanotubes, on the other hand, may have many dangling bonds. According to research carbon nanotubes having different tip structures may exhibit different chemical and physical properties (e.g. field emission properties, doping, etc). To realize the practical applications of carbon nanotubes, it is necessary to obtain carbon nanotubes with desired tip structures.
What is needed is to provide an apparatus and method for effectively synthesizing carbon nanotubes with desired tip structures.